Scientists from 99 countries issued a dire warning last month: curtail air pollution or expect drastic climate change in the next century.

The Earth's average surface temperature rose 1.1°F (.6°C) in the last century, according to the United Nation's Intergovernmental Panel on Climate Change (IPCC). The IPCC's January report predicts temperatures may rise as much as 11°F (5.8°C) in the next hundred years.

The bulk of global warming, say the IPCC scientists, as well as the resulting havoc wreaked on the world's ecosystems, can be blamed on human activity.

"In the next decade or two we really need to mobilize," said Will Burns of California's Pacific Institute for Studies in Development, Environment, and Security.

Burns said the IPCC report indicates that a 60 to 70 percent reduction in greenhouse gas emissions is needed in order to stabilize the level of pollutants in the airan amount that has doubled since the beginning of the Industrial Revolution.

"[The IPCC report] emphasizes what happens if we don't make those commitments," he said.

Although Burns called the 11° change predicted by the IPCC a "worst-case scenario," he said that the warming of the Earth has already begun.

A Changing Home

Carbon dioxide is an essential component of Earth's atmosphere. But since 1750, the gas's concentration has increased by 31 percent, the IPCC scientists note, reaching levels likely not exceeded in the past 20 million years.

An increased amount of greenhouse gases, including carbon dioxide, trap heat in the atmosphere, upping the Earth's average surface air temperature.

Scientists blame a myriad of effects on the Earth's land, water, and air on the temperature change.

According to the IPCC report, snow cover decreased ten percent since the late 1960s. The 20th century saw a "widespread retreat of mountain glaciers," the scientists write, and sea levels rose.

The scientists also blame changing weather patterns on global warming.

Looming Changes Threaten Humans

Long- and short-term effects of global warming will worsen as greenhouse gases are added to the atmosphere, warned Burns, and could have "horrific implications."

Each of these meteorological effects has the potential to dramatically affect life on Earth.

The loss of plant and animal species, "is one of the core long-term aspects of climate change," said Burns.

Marine species will be threatened by changing ocean temperatures, he said, resulting in a "catastrophic cascade in the food chain."

Land-dwelling animals, he added, will also be threatened, and may not be able to migrate fast enough to escape weather changes.

Humans, named as the primary cause of global warming, are not immune to its effects.

Burns said rising sea levels may result in the loss of small islands and "tremendous displacement of people in other coastal areas."

Warming may eventually change marine and terrestrial systems that humans depend on, said Burns. One model, he noted, predicts that 22nd-century Europe will become an arctic environment because "the system becomes overwhelmed."